Defoaming compositions and methods

ABSTRACT

The present invention provides improved defoaming compositions and methods. The compositions of the invention are basically comprised of polypropylene glycol, particulate hydrophobic silica and a liquid diluent.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to defoaming compositions and methods, andmore particularly, to such compositions and methods for preventing theformation of foam or breaking foam in well treating fluids.

2. Description of the Prior Art

Defoaming compositions and agents have long been used in the oil and gasindustry to prevent the formation of a foam or to destroy a previouslyformed foam. The defoaming compositions are commonly utilized ascomponents in well treating fluids to prevent the formation of foamduring the preparation and/or pumping of the treating fluids. Also,defoaming compositions have been utilized heretofore for breakingpreviously formed foamed well treating fluids. That is, when a stablefoamed well treating fluid must be disposed of on the surface, adefoaming composition is added to the fluid to destroy the foam wherebythe non-foamed components of the treating fluid can be readily disposedof.

A variety of defoaming compositions and agents have been utilizedheretofore. Examples of such defoaming compositions and agents utilizedin well treatment fluids include tributyl phosphate and acetylenic diolwhich are environmentally unsafe. Other prior art defoaming agents whichare environmentally safe include polypropylene glycol and a mixture ofpolypropylene glycol with a copolymer of ethylene oxide and propyleneoxide monomers. While these defoamers function adequately to prevent theformation of foam in well treating fluids when they are prepared andpumped, they do not function adequately for defoaming previously formedfoamed well treating fluids, and particularly, previously formed foamedwell cement slurries.

Thus, there is a continuing need for improved environmentally safedefoaming compositions for use in various fluids including welltreatment fluids.

SUMMARY OF THE INVENTION

The present invention provides improved environmentally safe defoamingcompositions and methods which meet the needs described above andovercome the deficiencies of the prior art. The compositions of theinvention are basically comprised of polypropylene glycol, particulatehydrophobic silica and a liquid diluent. While various liquid diluentscan be utilized, those which are particularly suitable include fattyacid methyl esters, olefins having one or more internal double bonds,alpha-olefins, polyalpha-olefins and linear paraffins.

A preferred defoaming composition of this invention is comprised ofpolypropylene glycol having a molecular weight of about 4,000 present inthe composition in an amount of about 30% by weight thereof, aparticulate hydrophobic silica comprised of silicone oil treatedprecipitated silica present in the composition in an amount of about 16%by weight thereof and an olefin having from about 11 to about 14 carbonatoms and one or more internal double bonds present in the compositionin an amount of about 54% by weight thereof.

A method of the present invention for preventing the formation of foamin a well treating fluid during its preparation or pumping into a wellbore comprises combining a defoaming composition of this invention withthe well treating fluid prior to preparing or pumping the fluid.

This invention also provides a method of defoaming a previously formedstable foamed well treating fluid by combining a defoaming compositionof this invention therewith.

It is, therefore, a principal object of the present invention to provideimproved defoaming compositions and methods.

Other and further objects, features and advantages of the invention willbe readily apparent to those skilled in the art upon a reading of thedescription of preferred embodiments which follows.

DESCRIPTION OF PREFERRED EMBODIMENTS

As mentioned above, defoaming compositions are commonly utilized in avariety of fluids to prevent the fluids from forming foam with air whenthey are agitated, mixed or the like in the presence of air. In thetreatment of wells with well treating fluids, the fluids are commonlymixed or blended in the presence of air on the surface and then pumpedinto the well bore. If the well treating fluids are inadvertently foamedwhile being mixed and pumped, adverse results can take place. Forexample, in completing and stimulating a well, unfoamed treating fluidsare often utilized which, if foamed, would not accomplish their intendedpurposes or would produce less than desirable results.

Some well treating fluids are intentionally formed into stable foams onthe surface in order to reduce the densities of the fluids or for otherreasons. When such stable foams must be disposed of on the surface, itis often necessary to break the foams in order to efficiently dispose ofthe non-foamed components. While defoaming compositions and agents havebeen developed and used successfully heretofore, such defoamingcompositions and agents generally have either been environmentallyunsafe or have produced less than desirable results when utilized tobreak previously formed stable foams. By the present invention, improveddefoaming compositions and methods are provided which areenvironmentally safe and also produce better defoaming results than theheretofore utilized defoaming compositions and agents.

The improved defoaming compositions of the present invention arebasically comprised of polypropylene glycol, particulate hydrophobicsilica and a liquid diluent. The polypropylene glycol utilized in thecompositions can have a molecular weight in the range of from about 425to about 4,000. It is preferred that the polypropylene glycol have amolecular weight at the high end of the above range, most preferablyabout 4,000. The polypropylene glycol is generally included in thedefoaming compositions of this invention in an amount in the range offrom about 20% to about 75% by weight of the compositions, mostpreferably about 30%.

A particulate hydrophobic silica useful in accordance with thisinvention is silicone oil treated precipitated silica. This hydrophobicsilica functions in combination with the polypropylene glycol to defoamfluids very efficiently. The precipitated silica can be prepared bysimultaneously adding sulfuric acid and sodium silicate solutions towater with agitation. The pH of the mixture during the reaction ismaintained above about 9 whereby smaller particles are continuouslydissolved during the precipitation of silica. As a result, uniformparticle sizes are obtained. During the precipitation process, theproperties of the silica can be varied by changing the ratio ofreactants, the reaction time, the reaction temperature and the reactionmixture concentrations. The suspension that results from theprecipitation process is filtered and dried followed by milling toreduce the size of agglomerates formed in the drying stage.

The precipitated silica is hydrophobized by spraying it with a uniformcoating of silicone oil followed by heating. The quantity of siliconeoil utilized is usually about 10% by weight of the precipitated silica.Particularly suitable silicone oil treated precipitated silica for usein accordance with this invention is commercially available under thetrade designations SIPERNET D-11™ and SIPERNET D-13™ from the DegussaCompany having a place of business in Chester, Pa. The SIPERNET D-11™has a BET surface area of 90 square centimeters per gram while theSIPERNET D-13™ has a BET surface area of 85 square centimeters per gram.Other properties of the products are the same and are as follows:average particle size—less than 5 microns; tapped density—120 grams perliter; pH—9.5 to 11.5; moisture loss at 105° C. after 2 hours—1.5%;ignition loss after 2 hours at 1,000° C.—5%; methanol wetability—greaterthan about 60%; SiO₂ content—98%; and NaSO₄ content—2%.

The particulate hydrophobic silica is generally included in thedefoaming compositions of this invention in an amount in the range offrom about 10% to about 20% by weight of the compositions, preferablyabout 16%.

A variety of liquid diluents which also function as dispersion mediumsfor the particulate hydrophobic silica can be utilized in accordancewith the present invention. Examples of preferred such liquid diluentsinclude, but are not limited to, fatty acid methyl esters, olefinshaving one or more internal double bonds, alpha-olefins,polyalpha-olefins and linear paraffins. Of these, olefins having fromabout 11 to about 14 carbon atoms and one or more internal double bondsare presently preferred. Generally, the liquid diluent is included inthe defoaming compositions of this invention in an amount in the rangeof from about 10% to about 70% by weight of the compositions, preferablyabout 54%.

Thus, a preferred defoaming composition of the present invention iscomprised of polypropylene glycol having a molecular weight in the rangeof from about 425 to about 4,000, particulate hydrophobic silica and aliquid diluent. The particulate hydrophobic silica is preferablysilicone oil treated precipitated silica.

A more preferred defoaming composition of this invention is comprised ofpolypropylene glycol having a molecular weight of about 4,000, siliconeoil treated precipitated silica and a liquid diluent selected from thegroup of fatty acid methyl esters, olefins having one or more internaldouble bonds, alpha olefins, polyalpha olefins and linear paraffins.

The most preferred composition of this invention is comprised ofpolypropylene glycol having a molecular weight of about 4,000 present inthe composition in an amount of about 30% by weight thereof, siliconeoil treated precipitated silica present in the composition in an amountof about 16% by weight thereof and a diluent comprised of an olefinhaving from about 11 to about 14 carbon atoms and one or more internaldouble bonds present in the composition in an amount of about 54% byweight thereof.

The methods of this invention include methods of preventing theformation of foam in a well treating fluid during its preparation orpumping into a well bore and methods of defoaming a previously formedstable foamed well treating fluid. More specifically, the methods of thepresent invention of preventing the formation of foam in a well treatingfluid during its preparation and pumping are basically comprised ofcombining a defoaming composition of this invention with said welltreating fluid, the defoaming composition being comprised ofpolypropylene glycol, particulate hydrophobic silica and a liquiddiluent. The methods of this invention for defoaming a previouslyprepared stable foamed well treating fluid are basically comprised ofcombining a defoaming composition with the foamed well treating fluid,the defoaming composition being comprised of polypropylene glycol,particulate hydrophobic silica and a liquid diluent.

As mentioned above, the defoaming compositions of this invention can beutilized in a variety of different fluids and are particularly wellsuited for use in well treating fluids. Examples of well treating fluidsin which the defoaming compositions can be utilized to prevent theformation of foam are aqueous gelled fluids and cement slurries. Anexample of a previously prepared foamed well treating fluid which can beefficiently defoamed using a defoaming composition of this invention isa stable foamed cement slurry. Excess previously prepared stable foamedcement slurries are often pumped into pits on the surface and must bedisposed of. By combining a defoaming composition of this invention withsuch foamed cement slurries, e.g., by spraying the defoaming compositionthereon, the foamed cement slurries, rapidly and completely breakwhereby they can be readily disposed of.

In order to further illustrate the defoaming compositions and methods ofthis invention, the following examples are given.

EXAMPLE 1

Test cement compositions were prepared from five different cementslurries containing various conventional additives, i.e., five cementcompositions without defoamer, fine cement compositions containing eachof four prior art defoamers and five cement compositions containing thedefoaming composition of the present invention. The components andquantities utilized in forming the five cement slurries are given inTable I below.

TABLE I Sodium Set Fluid Loss Crystalline Chloride, Weighting Retarder²,Control Dispersing Water, % Silica, % % by Agent¹, % % by Agent, %Agent⁴, % Slurry Premium by weight by weight weight of by weight weightof by weight by weight No. Cement of cement of cement water of cementcement of cement of cement 1 Yes 46 35 37.2 49 1 0.6³ — 2 Yes 38 — 37.2— 1 — — 3 Yes 35 — 35 — 1 0.05⁵ 0.3 4 Yes 61 — — — — 1.06⁶ — 5 Yes 46 —— — — 0.8³ — ¹The weighting agent used was iron oxide. ²The set retarderwas comprised of modified lignosulfonate. ³The fluid loss control agentwas hydroxyethylcellulose. ⁴The dispersing agent was the condensationproduct of formaldehyde, acetone and sodium bisulfate. ⁵The fluid losscontrol agent was comprised of carboxymethylhydroxyethylcellulose. ⁶Thefluid loss control agent was comprised of a modified copolymer of AMPS ®and N,N-dimethylacrylamide.

The theoretical design density of each of the test cement compositionsas well as the densities of each test cement composition which did notinclude a defoamer, each test composition including a prior art defoamerand each test composition including the defoaming composition of thepresent invention were determined and are given in Table II below. Whenincluded, the defoamers were added to the test cement compositions inamounts of 0.25% by weight of cement.

TABLE II Design No Prior Art Prior Art Prior Art Prior Art DefoamingComposition of the Slurry Density, Defoamer, Defoamer¹, Defoamer²,Defoamer³, Defoamer⁴, Present Invention⁵, No. lb/gal lb/gal lb/gallb/gal lb/gal lb/gal lb/gal 1 19.2 17.3 18.75 18.4 18.85 18.6 18.8 216.8 13.2 16.7 16.7 16.65 16.7 16.65 3 16.4 12.8 16.15 15.6 16.3 16.216.3 4 14.4 13.4 14.4 14.4 14.4 14.4 14.4 5 15.6 14.9 15.6 15.6 15.615.6 15.6 ¹Tributyl phosphate ²Acetylenic diol ³Polypropylene glycolmixed with copolymer of ethylene oxide and propylene oxide⁴Polypropylene glycol ⁵Propylene glycol (MW = 4,000) - 30%, silicone oiltreated precipitated silica - 16% and C₁₁-C₁₄ olefin with internaldouble bonds - 54%, all by weight of composition.

From Table II it can be seen that the defoaming composition of thepresent invention substantially equaled or exceeded the defoamingefficiencies of the conventional defoamers. That is, the defoamingcomposition of the present invention prevented the formation of foam inthe test cement compositions to a substantially equal or greater degreethan the prior art defoamers tested.

EXAMPLE 2

Stable foamed test cement compositions were prepared containing variousprior art defoamers and the defoaming composition of the presentinvention. The test cement compositions contained the followingcomponents: Premium cement; a fluid loss control agent comprised ofcarboxymethylhydroxyethylcellulose in an amount of 0.3% by weight ofcement; water in an amount of 43% by weight of cement; a foaming agentcomprised of an ethoxylated alcohol sulfate in an amount of 1.5% byvolume of water; a foam stabilizer comprised of cocoamidopropylbetainein an amount of 0.75% by volume of water; and 1.2% of defoamer by weightof foamed slurry. The unfoamed test compositions had a density of 15.91lbs. per gallon and after being foamed, the compositions had a densityof 10.5 lbs. per gallon. The density of each test cement composition wasdetermined and the results are given below.

Cement Composition Defoamer Density, lb/gal tributyl phosphate 12.39acetylenic diol 11.91 polypropylene glycol mixed 10.75 with copolymer ofethylene oxide and propylene oxide polypropylene glycol 10.65 presentinvention (same as 15.8  footnote 5, Table II)

From the above, it can be seen that the defoaming composition of thisinvention is highly efficient in defoaming stable foamed fluids.

The procedure described in Example 2 utilizing the foamed cement slurrydescribed therein was repeated using a defoaming composition of thepresent invention (footnote 5, Table II) including a linear alpha-olefinhaving from about 11 to about 14 carbon atoms as the liquid diluentinstead of the olefin having internal double bonds. A second test wasalso conducted using a linear paraffin having from about 11 to about 14carbon atoms as the liquid diluent. The results of these tests are givenbelow.

Defoamer Density, lb/gal present invention, but 15.85 including linearalpha- olefin diluent present invention, but 15.8  including linearparaffin diluent

From the above, it can be seen that various liquid diluents can beutilized in the compositions of this invention without changing theeffectiveness of the compositions.

EXAMPLE 3

A base cement slurry comprised of Premium cement, the defoamingcomposition of the present invention (footnote 5, Table II) in an amountof 1% by weight of cement, and water in an amount of 46% by weight ofcement was prepared. Three different fluid loss additives were combinedwith three test portions of the base cement slurry and the viscosity andfluid loss for each test portion was determined in accordance with theprocedures set forth in the API Specification For Materials And TestingFor Well Cements, API Specification 10, 5th Edition, dated Jul. 1, 1990,of the American Petroleum Institute. The results of these tests aregiven in Table III below.

TABLE III 125° F. Fluid Quantity, Fluid Loss Loss % by at 1,000 125° F.Viscosity, Additive weight of psi, cc/30 Bc Used cement min. Initial 20min. A¹ 1.2 36 8 9 B² 0.6 20 10 12 C³ 1.2 34 9 7 ¹Fluid Loss Additive Awas comprised of modified hydroxyethylcellulose. ²Fluid Loss Additive Bwas comprised of a modified copolymer of AMPS ® andN,N-dimethylacrylamide. ³Fluid Loss Additive C washydroxyethylcellulose.

From the results given in Table III it can be seen that the presence ofthe defoaming composition of the present invention did not materiallyaffect the viscosities or fluid losses of the cement slurries.

EXAMPLE 4

A base cement slurry comprised of premium cement, water in an amount of46% by weight of cement, a fluid loss additive comprised of a modifiedcopolymer of AMPS® and N,N-dimethylacrylamide in an amount of 0.6% byweight of cement and a set retarder comprised of a modifiedlignosulfonate in an amount of 0.2% by weight of cement was prepared. Toone portion of the base cement slurry, the defoaming composition of thisinvention (footnote 5, Table II) was added in an amount of 1% by weightof cement. No defoamer was added to a second portion of the base slurry.The test portions of the base slurry were subjected to thickening timetests conducted in accordance with the above mentioned API Specification10. The results of these tests are set forth below.

140° F. BHCT, 5200 psi, Defoamer of the Casing Schedule 5 g, timePresent Invention to reach 70 Bc (hr:mn) No 6:39 Yes 5:36

From the above results, it can be seen that the presence of thedefoaming composition of the present invention had little or no effecton cement slurry thickening time.

Thus, the present invention is well adapted to carry out the objects andattain the ends and advantages mentioned as well as those which areinherent therein. While numerous changes may be made by those skilled inthe art, such changes are encompassed within the spirit of thisinvention as defined by the appended claims.

What is claimed is:
 1. A method of preventing the formation of foam in awell treating fluid during its preparation and pumping into a well borecomprising combining a defoaming composition with said well treatingfluid during its preparation, said defoaming composition being comprisedof polypropylene glycol, particulate hydrophobic silica and a liquiddiluent.
 2. The method of claim 1 wherein said polypropylene glycol ispresent in said composition in an amount in the range of from about 20%to about 75% by weight thereof.
 3. The method of claim 1 wherein saidparticulate hydrophobic silica is silicone oil treated precipitatedsilica and is present in said composition in an amount in the range offrom about 10% to about 20% by weight thereof.
 4. The method of claim 1wherein said liquid diluent is comprised of an olefin having from about11 to about 14 carbon atoms and one or more internal double bonds and ispresent in said composition in an amount in the range of from about 10%to about 70% thereof.
 5. The method of claim 1 wherein saidpolypropylene glycol has a molecular weight of about 4,000 and ispresent in said composition in an amount of about 30% by weight thereof.6. The method of claim 5 wherein said particulate hydrophobic silica issilicone oil treated precipitated silica and is present in saidcomposition in an amount of about 16% by weight thereof.
 7. The methodof claim 6 wherein said liquid diluent is comprised of an olefin havingfrom about 11 to about 14 carbon atoms and one or more internal doublebonds and is present in said composition in an amount of about 54% byweight thereof.
 8. A method of defoaming a previously prepared stablefoamed well treating fluid comprising combining a defoaming compositionwith said foamed well treating fluid, said defoaming composition beingcomprised of polypropylene glycol, particulate hydrophobic silica and aliquid diluent.
 9. The method of claim 8 wherein said polypropyleneglycol is present in said composition in an amount in the range of fromabout 20% to about 75% by weight thereof.
 10. The method of claim 8wherein said particulate hydrophobic silica is silicone oil treatedprecipitated silica and is present in said composition in an amount inthe range of from about 10% to about 20% by weight thereof.
 11. Themethod of claim 8 wherein said liquid diluent is comprised of an olefinhaving from about 11 to about 14 carbon atoms and one or more internaldouble bonds and is present in said composition in an amount in therange of from about 10% to about 70% thereof.
 12. The method of claim 8wherein said polypropylene glycol has a molecular weight of about 4,000and is present in said composition in an amount of about 30% by weightthereof.
 13. The method of claim 12 wherein said particulate hydrophobicsilica is silicone oil treated precipitated silica and is present insaid composition in an amount of about 16% by weight thereof.
 14. Themethod of claim 13 wherein said liquid diluent is comprised of an olefinhaving from about 11 to about 14 carbon atoms and one or more internaldouble bonds and is present in said composition in an amount of about54% by weight thereof.